Continuum constitutive laws to describe acoustic attenuation in glasses.

Nowadays metamaterials are at the focus of an intense research as promising for thermal and acoustic engineering. However, the computational cost associated to the large system size required for correctly simulating them imposes the use of finite-elements simulations, developing continuum models, able to grasp the physics at play without entering in the atomistic details. Still, a correct description should be able to reproduce not only the extrinsic scattering sources on waves propagation, as introduced by the metamaterial microstructure, but also the intrinsic wave attenuation of the material itself. This becomes dramatically important when the metamaterial is made out of a glass, which is intrinsically highly dissipative and with a wave attenuation strongly dependent on frequency. Here we propose a continuum mechanical model for a viscoelastic medium, able to bridge atomic and macroscopic scale in amorphous materials and describe phonon attenuation due to atomistic mechanisms, characterized by a defined frequency dependence. This represents a first decisive step for investigating the effect of a complex nano- or microstructure on acoustic attenuation, while including the atomistic contribution as well.

Enhancement and anticipation of the Ioffe-Regel crossover in amorphous/nanocrystalline composites.

Nanocomposites made of crystalline nanoinclusions embedded in an amorphous matrix are at the forefront of current research for energy harvesting applications. However, the microscopic mechanisms leading alternatively to an effectively reduced or enhanced thermal transport still escape understanding. In this work, we present a molecular dynamics simulation study of model systems, where for the first time we combine a microscopic investigation of phonon dynamics with the macroscopic thermal conductivity calculation, to shed light on thermal transport in these materials. We clearly show that crystalline nanoinclusions represent a novel scattering source for vibrational waves, modifying the nature of low energy vibrations and significantly anticipating the propagative-to-diffusive crossover (Ioffe-Regel), usually located at energies of few THz in amorphous materials. Moreover, this crossover position can be tuned by changing the elastic contrast between nanoinclusions and the matrix, and anticipated by a factor as large as 10 for a harder inclusion. While the propagative contribution to thermal transport is drastically reduced, the calculated thermal conductivity is not significantly affected in the chosen system, as the diffusive contribution dominates heat transport when all phonons are thermally populated. These findings allow finally to understand the panoply of contradictory results reported on thermal transport in nanocomposites and give clear indications to the characteristics that the parent phases should have for efficiently reducing heat transport in a nanocomposite.

Propagative and diffusive regimes of acoustic damping in bulk amorphous material.

In amorphous solids, a non-negligible part of thermal conductivity results from phonon scattering on the structural disorder. The conversion of acoustic energy into thermal energy is often measured by the dynamical dtructure factor (DSF) thanks to inelastic neutron or x-ray scattering. The DSF is used to quantify the dispersion relation of phonons, together with their damping. However, the connection of the dynamical structure factor with dynamical attenuation of wave packets in glasses is still a matter of debate. We focus here on the analysis of wave-packet propagation in numerical models of amorphous silicon. We show that the damped harmonic oscillator model fits of the dynamical structure factors give a good estimate of the wave packets mean free path, only below the Ioffe-Regel frequency. Above the Ioffe-Regel frequency and below the mobility edge, a pure diffusive regime without a definite mean free path is observed. The high-frequency mobility edge is characteristic of a transition to localized vibrations. Below the Ioffe-Regel frequency, a mixed regime is evidenced at intermediate frequencies, with a coexistence of propagative and diffusive wave fronts. The transition between these different regimes is analyzed in detail and reveals a complex dynamics for energy transport, thus raising the question of the correct modeling of thermal transport in amorphous materials.

New Simplified Screening Method for Postprandial Hypotension in Older People.

BACKGROUND: Postprandial hypotension (PPH) is an important disorder in the older people that remain underdiagnosed. The reference PPH diagnostic method is too demanding, because blood pressure (BP) needs to be measured 8 times in 2 hours. OBJECTIVES: Our primary objective was to define a new simplified PPH diagnostic method and to evaluate its performances. DESIGN: We conducted a cross-sectional study. SETTING: Two geriatric rehabilitation units in France. PARTICIPANTS: 104 patients (70 women, 34 men) with high risk of PPH were included. MEASUREMENTS: BP was measured twice before the midday meal in seated position at the table, and every 15 minutes for 90 minutes after the end of the meal. Receiver Operating Characteristic curves were plotted for each postprandial BP measure to determine the best postprandial measure in terms of sensitivity and specificity. The optimal diagnostic threshold was calculated with Youden's index according to BP difference before and after the meal. RESULTS: A new simplified diagnostic method is proposed: a decrease of at least 10 mmHg systolic BP between BP measures before the meal and 75 minutes after the end of the meal. This new method had a sensitivity of 82% (95%CI 66 - 92) and a specificity of 91% (95%CI 81 - 97). CONCLUSION: This new diagnostic method is fast, efficient and suitable for everyday use. It could improve PPH diagnosis in older people. Larger studies are needed to validate it.

Mapping between atomistic simulations and Eshelby inclusions in the shear deformation of an amorphous silicon model.

In this paper we perform quasistatic shear simulations of model amorphous silicon bulk samples with Stillinger-Weber-type potentials. Local plastic rearrangements identified based on local energy variations are fitted through their displacement fields on collections of Eshelby spherical inclusions, allowing determination of their transformation strain tensors. The latter are then used to quantitatively reproduce atomistic stress-strain curves, in terms of both shear and pressure components. We demonstrate that our methodology is able to capture the plastic behavior predicted by different Stillinger-Weber potentials, in particular, their different shear tension coupling. These calculations justify the decomposition of plasticity into shear transformations used so far in mesoscale models and provide atomic-scale parameters that can be used to limit the empiricism needed in such models up to now.

Impact of pressure on plastic yield in amorphous solids with open structure.

Plasticity in amorphous silica is unusual: The yield stress decreases with hydrostatic pressure, in contrast to the Mohr-Coulomb response commonly found in more compact materials such as bulk metallic glasses. To better understand this response, we have carried out molecular dynamics simulations of plastic response in a model glass with open structure. The simulations reproduce the anomalous dependence of yield stress with pressure and also correctly predict that the plastic response turns to normal once the material has been fully compacted. We also show that the overall shape of the yield surface is consistent with a quadratic behavior predicted assuming local buckling of the structure, a point of view that fits well into the present understanding of the deformation mechanisms of amorphous silica. The results also confirm that free volume is an adequate internal variable for a continuum scale description of the plastic response of amorphous silica. Finally, we also investigate the long-range correlations between rearrangement events. We find that strong intermittency is observed when the structure remains open, while compaction results in more homogeneous rearrangements. These findings are in agreement with recent results on the effect of compression on the middle range order in silicate glasses and also suggest that the well-known volume recovery of densified silica at relatively low temperatures is in fact a form of aging.

Boson peak and Ioffe-Regel criterion in amorphous siliconlike materials: The effect of bond directionality.

The vibrational properties of model amorphous materials are studied by combining complete analysis of the vibration modes, dynamical structure factor, and energy diffusivity with exact diagonalization of the dynamical matrix and the kernel polynomial method, which allows a study of very large system sizes. Different materials are studied that differ only by the bending rigidity of the interactions in a Stillinger-Weber modelization used to describe amorphous silicon. The local bending rigidity can thus be used as a control parameter, to tune the sound velocity together with local bonds directionality. It is shown that for all the systems studied, the upper limit of the Boson peak corresponds to the Ioffe-Regel criterion for transverse waves, as well as to a minimum of the diffusivity. The Boson peak is followed by a diffusivity's increase supported by longitudinal phonons. The Ioffe-Regel criterion for transverse waves corresponds to a common characteristic mean-free path of 5-7 Å (which is slightly bigger for longitudinal phonons), while the fine structure of the vibrational density of states is shown to be sensitive to the local bending rigidity.

Factors associated with an increased risk of vertebral fracture in monoclonal gammopathies of undetermined significance.

Monoclonal gammopathies of undetermined significance (MGUS) have been shown to be associated with an increased risk of fractures. This study describes prospectively the bone status of MGUS patients and determines the factors associated with vertebral fracture. We included prospectively 201 patients with MGUS, incidentally discovered, and with no known history of osteoporosis: mean age 66.6±12.5 years, 48.3% women, 51.7% immunoglobulin G (IgG), 33.3% IgM and 10.4% IgA. Light chain was kappa in 64.2% patients. All patients had spinal radiographs and bone mineral density measurement in addition to gammopathy assessment. At least one prevalent non-traumatic vertebral fracture was discovered in 18.4% patients and equally distributed between men and women. Fractured patients were older, had a lower bone density and had also more frequently a lambda light chain isotype. Compared with patients with κ light chain, the odds ratio of being fractured for patients with λ light chain was 4.32 (95% confidence interval 1.80-11.16; P=0.002). These results suggest a high prevalence of non-traumatic vertebral fractures in MGUS associated with lambda light chain isotype and not only explained by low bone density.

Rheological properties vs. local dynamics in model disordered materials at low temperature.

We study the rheological response at low temperature of a sheared model disordered material as a function of the bond rigidity. We find that the flow curves follow a Herschel-Bulkley law, whatever is the bond rigidity, with an exponent close to 0.5. Interestingly, the apparent viscosity can be related to a single relevant time scale t rel, suggesting a strong connection between the local dynamics and the global mechanical behaviour. We propose a model based on the competition between the nucleation and the avalanche-like propagation of spatial strain heterogeneities. This model can explain the Herschel-Bulkley exponent on the basis of the size dependence of the heterogeneities on the shear rate.

Results of a Prospective Study of High-Dose or Conventional Anthracycline-Cyclophosphamide Regimen Plus Radiotherapy for Localized Adult Non-Hodgkin's Primary Bone Lymphoma.

Background. Primary bone lymphoma (PBL) is a rare entity that has only been reviewed in one prospective and small retrospective studies, from which it is difficult to establish treatment guidelines. We prospectively evaluated high-dose or conventional anthracycline-cyclophosphamide dose and radiotherapy for PBL. Patients and Methods. The GOELAMS prospective multicenter study (1986-1998) enrolled adults with localized high-grade PBL according to age and performance status (PS). Patients <60 years received a high-dose CHOP regimen (VCAP) and those ≥60 years a conventional anthracycline-cyclophosphamide regimen (VCEP-bleomycin); all received intrathecal chemotherapy and local radiotherapy. Results. Among the 26 patients included (VCAP: 19; VCEP-bleomycin: 7), 39% had poor PS ≥2. With a median follow-up of 8 years, overall survival, event-free survival, and relapse-free survival were 64%, 62%, and 65%, respectively, with no significant difference between treatment groups. Poor PS was significantly associated with shorter OS and EFS. Conclusions. Our results confirm the efficacy of our age-based therapeutic strategy. High-doses anthracycline-cyclophosphamide did not improve the outcome. VCEP-bleomycin is effective and well tolerated for old patients. The intensification must be considered for patients with PS ≥2, a poor prognostic factor.

Treatment-limiting decisions, comorbidities, and mortality in the emergency departments: a cross-sectional elderly population-based study.

BACKGROUND: Older adults experience a higher risk of death in the emergency departments (EDs), in part, as a result of their comorbidities. A treatment-limiting decision is often reported for older adults who die in the EDs. The Charlson Comorbidity Index (CCI) is a validated method for the scoring of comorbidities. Whether an association between the CCI and treatment-limiting decisions exists remains unknown. OBJECTIVE: To determine whether the CCI was associated with the treatment-limiting decisions made for older patients who die in the EDs. METHODS: A total of 2,095 patients ≥65 years old who died in the EDs in France and Belgium were prospectively included between 2004 and 2005. The recorded data included: 1) the CCI score; 2) patient age; 3) gender; 4) living in senior housing facilities; 5) hospitalizations occurring in the previous year; 6) presence of functional limitations (according to the Knaus classification); 7) chronic diseases; and 8) presence of organ failure(s). A treatment-limiting decision was defined as a predetermined choice not to implement therapies that would otherwise be required to sustain life. RESULTS: A treatment-limiting decision was identified in 993 (47%) patients. Fully-adjusted logistic regression model showed that a CCI ≥ 5 (OR=25.56 with P=0.037), age ≥85years (OR=20.33 with P<0.001), living in an institution (OR=0.15 with P=0.017), hematologic (OR=6.92 with P=0.020) and respiratory disease (OR=0.17 with P=0.046), and neurologic causes (OR=0.20 with P=0.010) of organ failure were significantly associated with treatment-limiting decisions. CONCLUSION: An elevated CCI score (≥5) was associated with a treatment-limiting decision in elderly patients evaluated in the EDs. Further research is needed to corroborate this finding.

Role of local order in the small-scale plasticity of model amorphous materials.

The mechanism of plastic flow in amorphous solids involves nucleation-controlled shear transformations, triggered under stress from fertile sites. However, the origin of these sites is still a matter of debate. In this paper, we show that the connection between local plastic activity and coordination defects in amorphous systems depends on the nature of the interatomic interactions. In particular, the directionality of the bonds, as quantified by the three-body term in Stillinger-Weber-like interactions, affects not only the role of local defects, but also the size of the plastic rearrangements, and the global stress-strain behavior. We study the effect of structure changes due to different quenching rates as well. We conclude the paper by a comparison between amorphous plasticity and the Peierls-Nabarro theory of plasticity in crystals.

Partial characterization of the gene encoding myoadenylate deaminase from the teleost fish Platichthys flesus.

AMP-deaminase (AMPD, EC 3.5.4.6), which catalyzes the irreversible hydrolytic deamination of AMP to IMP and ammonia, is an important energy-related enzyme. The partial genomic sequence of the gene encoding myoadenylate deaminase (AMPD1) from the teleost fish Platichthys flesus was determined. The amino acid sequence of P. flesus AMPD1 shows 82% homology with that of the teleost fish Danio rerio. Comparison of genomic sequences of P. flesus and Rattus norvegicus reveals a high degree of conservation of both sequence and structural organization. A phylogenetic analysis of AMPD sequences shows that bony fish and mammalian AMPD1s arise by duplication of a common primordial gene.

Development of isohomoeoallelic lines within the wheat cv. Courtot for high molecular weight glutenin subunits: transfer of the Glu-D1 locus to chromosome 1A.

Wheat quality depends on protein composition and grain protein content. High molecular weight glutenin subunits (HMW-GS) play an important role in determining the viscoelastic properties of gluten. In an attempt to improve the bread-making quality of hexaploid wheat by elaborating novel HMW-GS combinations, a fragment of wheat chromosome 1D containing the Glu-D1 locus encoding the Dx2+Dy12 subunits was translocated to the long arm of chromosome 1A using the ph1b mutation. The partially isohomoeoallelic line selected was characterized using cytogenetical and molecular approaches to assess the amount of chromatin introgressed in the translocated 1A chromosome. Triple-target genomic in situ hybridization indicated that the translocated 1A chromosome had a terminal 1D segment representing 25% of the length of the recombinant long arm. The translocation was also identified on the long arm using molecular markers, and its length was estimated with a minimum of 91 cM. Proteome analysis was performed on total endosperm proteins. Out of the 152 major spots detected, 9 spots were up-regulated and 4 spots were down-regulated. Most of these proteins were identified as alpha-, beta-, gamma-gliadins assigned to the chromosomes of homoeologous groups 1 and 6. Quantitative variations in the HMW-GS were only observed in subunit Dy12 in response to duplication of the Glu-D1 locus.

Existence of a rotational axial component in the human humeral medullary canal.

To explain surgical findings, we studied the anatomy of the human humeral medullary canal on a series of 28 bones in 16 patients and 9 dried bones. A methodology is described to find angle of medullary canal on CT scans regarding to an epicondylar reference axis. We found a constant tri-dimensional spiral shape of the medullary canal in the distal part of the bone. The relations between this first description and the literature are discussed.